Sorry your wrong. First off, of course super powers can go protectionist and impose tariffs on individual countries. We do this all the time, think Iran, think Russia.
Yes some farmers are taking a hit right now, some due to the wet spring and others due to the trade war. Yes, we are trying to use part of the tariff money about $5 billion a month to offset the loses to farmers. This will be short term as markets reset.
Yes, Chinese and foreign manufacturers were moving out before the tariffs and some due to rising world competition and higher Chinese labor cost. But low end Chinese companies also moved because of the rising problem of keeping skilled workers. Which they still haven't figured out how to resolve. Skilled workers migrate to the higher paying tech level jobs. This creates a skilled worker vacuum going down the supply lines. But the latest moves out of China are the result of tariffs being the latest straw to seek other manufacturing sources.
China is making a big and dumb mistake getting into a trade war with the USA. It can't win. You'll see. Our economy is growing due to our internal expansion and China's economy isn't growing because they are primarily a export economy. China has been trying for years to develop an internal economy and although its larger it can't support its manufacturing. Why do you think China made its moves towards Hong Kong now? China's internal problems are increasing.
Of course China pays for the tariffs. Do you even know how trade works? Companies will seek cheaper sources of goods and material as Chinese prices increase due to the tariffs.
As far as China treasury holdings. The buying of treasuries gives China a source of dollars they can use to buy our goods without paying a fee to change Renminbi into dollars.